Doesn't matter how much of their own token founders buy at an IPO, it is cheating anyway. The more the founders cheat, the greater the impact will be. NXT IPO btw probably was free of that, otherwise their IPO would collect more funds.
It's perfectly OK however if the founders buy their token after the IPO.
In this crypto world, so far, there are two ways for devs to own the coins from the crowd sale. One is the devs set aside a big chunk of the coins for themselves for the future development and awards. Another is to participate the crowd sale by themselves.
Ethereum did both. They set aside a chunk of ethers for themselves and allow devs to buy in the crowd sale. But they set a kind of limit for their devs. However on one can monitor it. The Augur team did the same in their crowd sale.
Iota team decideed to not set aside a chunk of coins for themselves and their devs have to buy if they want to own some coins. What else can you ask?